1. Field
The present invention relates to a brake fluid pressure control device for vehicle.
2. Description of the Related Art
A brake fluid pressure control device for a vehicle, which controls hydraulic pressure of brake fluid in wheel cylinders, is provided therein with a base unit which is assembled therein with electronic valves, motors, plunger pumps, and a control circuit board that controls the electronic valves to open and close and controls the motor.
In the brake fluid pressure control device for a vehicle, the base unit is formed therein with fluid passages for communicating master cylinders and wheel cylinders. The brake fluid pressure control device controls the electronic valves or the motors operate in accordance with an operation of a vehicle, to thereby vary hydraulic pressures of brake fluid in fluid passages.
The base unit of the brake fluid pressure control device for a vehicle is provided with valve mounting holes which are mounted therein with inlet valves or outlet valves, reservoir holes mounted with reservoirs and cylinder holes into which plungers of plunger pumps are inserted, and the outlet valve mounting holes are communicated at a middle portion of a suction hole which becomes fluid passage for making the cylinder holes communicate with the reservoir holes. An example of a conventional brake fluid pressure control device is disclosed in Japanese Patent No. 3701669 (counterpart international patent application is published as WO/1994/008830).
In this configuration, when the outlet valve is opened, brake fluid flows into the reservoir through the suction hole from the outlet valve, and when plunger pump operates in a state of the outlet valve closed, brake fluid in the reservoir is suctioned into the plunger pump through the suction hole.
Such a conventional base unit employs the same fluid passage (suction hole), which used in order for a plunger pump to suck a brake fluid from a reservoir, as that fluid passage which is used to make a brake fluid flow into the reservoir, and accordingly it cannot make the cross-sectional area (inside diameter) of the fluid passage change. Accordingly, there are less degree of freedom for designing a fluid passage within a base unit.
For example, to enhance efficiency of a plunger pump, it is preferable that the cross-sectional area of a suction hole communicating with a reservoir is enlarged. However, in a conventional brake fluid pressure control device for a vehicle, two seal members are mounted to a piston of a plunger pump and a suction valve is arranged between the two seal members. Accordingly, since the diameter of the suction hole (cross-sectional area) is dependent on a slip-movement amount of a plunger pump, the diameter of the suction hole may not be enlarged beyond a limited size.